a) Field of the Invention
The present invention is directed to an arrangement by means of which the image field of the illumination components and irradiation components of ophthalmic instruments for diagnosis and therapy is improved. The arrangement is suitable in particular for ophthalmic instruments in which it is important to achieve a uniformly high image quality over broad regions of the eye.
b) Description of the Related Art
This is the case, for example, in slit lamps. A light section is generated in the interior of the eye being examined by means of slit image projection. To ensure an exact evaluation of the section images generated in this way, a sharp imaging of the slit image is required on the visual axis as well as in the edge areas of the eye.
The present arrangement for improving the image field is usable, in principle, wherever a uniformly high image quality must be ensured over a broad area. Other applications apart from ophthalmology include, for example, laser medicine, refractive surgery and irradiation of an optical lens that is changeable by means of light according to Patents WO 00/41650 and WO 01/71411.
In this type of lens comprising a matrix of different plastics, polymerization processes are triggered by irradiation resulting in a change in the refractive index or in the shape of the lens. Intraocular lenses (IOL) of this type can be changed after implantation through directed irradiation in such a way that defective vision can be improved.
In slit lamps such as those described in [1], mechanical/optical elements such as slit diaphragms are used predominantly for generating slit images. It is difficult to achieve the variable, very small slit widths that are required for high optical detail resolution within the optical section. Further, the alignment of the mechanical subassemblies is very complicated and is made even more difficult by the thermal expansion of the subassemblies. It is almost impossible to reproduce exact slit widths. Since the slit image projection entails optical imaging with a physically limited depth of field, the image must always be focused strictly on the point of examination. A section bundle that is focused over the entire extent of the human eye cannot be achieved by the previously known solutions.
DE 198 12 050 A1 describes a method and an arrangement for the illumination in an ophthalmic microscope. A wide variety of light mark geometries is generated by means of optoelectronic components. The light field geometries are projected on the anterior and posterior portions of the eye and are used for general examination of the eye.
DE 199 43 735 A1 describes a method and an arrangement for directed irradiation of an eye by means of light from the visible and/or near infrared wavelength range. The irradiation produces irreversible chemical changes in the eye lens substance resulting in a change in the refractive index and/or in the transmission characteristics for the visible effective radiation so that it is possible to improve defective vision. For successful treatment, the distribution of the refractive power of the eye to be treated must be determined as continuously and completely as possible. The desired refractive power distribution following treatment and the data about the irradiation which is required for this are determined from these values. In this solution, it is disadvantageous that the irradiation can generally only be carried out successively point by point so that the treatment process is time-consuming. Therefore, fixation of the eyeball for the duration of treatment is indispensable.
U.S. Pat. Nos. 5,404,884; 5,139,022; and 6,275,718 describe methods and arrangements for the illumination of the anterior eye segments in which a laser with a planar configuration is used as light source. These solutions are disadvantageous in that the variability of the light field geometries is limited. Further, the system for receiving the scattered light from the eye has a physically limited depth of field which cannot fully acquire the area over which the sharp laser section image extends.
Reference:
    [1]Rassow, B., et al., “Ophthalmologisch-optische Instrumente [Ophthalmic optical instruments]”, 1987, Ferdinand Enke Verlag Stuttgart, pages 99 ff. and 137 ff.
In current ophthalmic instruments, the straight or even oppositely curved image planes of the illumination components and irradiation components have a disadvantageous effect. The structures projected in or on the eye have the required image sharpness at the visual axis only in the center of the image field. In the outer areas and edge areas, the fine structures fan out, become blurred and lose intensity to an appreciable extent. Accordingly, evaluation of the distortion of the structures is made harder or is only possible within a limited area.